Blends of ANFO and slurry explosives are known and have been used commercially for about 15 years. Such blends contained up to about 50 wt. % ANFO in the blend and were suitable for use in large diameter boreholes, e.g. about 20 cm in diameter or greater. In recent years it has been found that higher percentages of ANFO in the blend could be used, e.g. up to about 85-90 wt. % ANFO. While blends with about 80-90 wt. % ANFO tend to have greater blasting power than the earlier blends of ANFO, they tend to have similar physical characteristics to ANFO, e.g. they retain the dry flowable characteristics, and retain the characteristic of being relatively easily desensitized by water. Such desensitization may occur as a result of attack by water when the explosive is in the borehole, or it may occur over a period of time because of migration of water from the slurry portion of the blend to the ANFO portion. Lack of water resistance or lack of "shelf stability" of the blend may lead to poor blasting characteristics. Methods for "waterproofing" ammonium nitrate or ANFO have been disclosed in a number of publications.
U.S. Pat. No. 2,537,039 relates to gelatinous compositions, e.g. ammonia dynamites, with various tackifying agents. A)so disclosed are certain non-nitroglycerin gelatinous explosives, including one comprising 97.0% ammonium nitrate and 3.0% of a non-explosive gel, containing 95% petrolatum and 5% polyisobutylene having a molecular weight of 80,000.
U.S. Pat. No. 3,160,536 relates to explosive mixtures of granular ammonium nitrate, a liquid hydrocarbon and a metallic soap. The hydrocarbon and metallic soap form a substance having a gel-like consistency with which to coat the ammonium nitrate, thus rendering the mixture hydrophobic and permitting packaging in a water-impervious flexible plastic container.
U.S. Pat. No. 3,287,189 relates to grease-coated porous, particulate ammonium nitrate explosive compositions which are formed by dusting or otherwise blending particulate porous ammonium nitrate, for example prilled or ground ammonium nitrate, with from about 0.5 to about 2 wt. % of a finely divided alkali or alkaline earth metal salt of an aliphatic carboxylic acid of 8 to 24 carbon atoms. The grease-coated ammonium nitrate may then be mixed with fuel oil to form an explosive composition. Alternatively, the ANFO may be mixed with an aqueous ammonium nitrate solution containing a thickening agent, e.g. guar gum, to provide an aqueous slurry explosive containing from 3 to 15 wt. % water. Part of the ammonium nitrate is first mixed with a grease composition and a selected hydrocarbon fuel oil prior to being added to the aqueous solution. Such slurry explosives are characterized as ranging from a pourable slurry to a thick paste to provide a protective water-resistance grease coating in the pores of, and on the particles of, the ammonium nitrate.
U.S. Pat. No. 3,919,016 discloses a process for thickening hydrocarbon oil slurries of ammonium nitrate with a latex of an elastomer which is inverted into the nitrate slurry. One of the latices disclosed contains from about 5 to 75 wt. % cis-1,4-polyisoprene and polyisobutylene, 25 to 75 wt. % water and 0.01 to 5 wt. % water-soluble surfactant.
U.S. Pat. No. 4,278,480 relates to slurry explosives which are permanently tacky and which may be adhesively applied to surfaces to be blasted. Particulate ammonium nitrate is mixed with a polymer comprising a pourable isobutylene, which is semi-solid but fluent at room temperature. The explosives exemplified include polyisobutylene at concentrations of from 20 to 25 wt. % .